Oscilloscope display method and circuit for f. m. radar systems



Nov. 11, 1958 T. c. PRIDMORE ET AL OSCILLOSCOPE DISPLAY METHOD AND CIR-CUIT FOR F'. M. RADAR SYSTEMS Filed Deo. 15, 1955 4 5 Sheets-Sheet l ATTORNEYS Nov. 11, 1958 T. c. PRIDMORE ET AL oscILLoscoPE DISPLAY METHOD AMD CIRCUIT FOR I. M. RADAR SYSTEMS 3 Sheets-Sheet 2 Filed Deo. l5, 1955 INVENTORS THOMAS 6I PF? /DMOIE GORDON S. LE Y ATTORNEYS T. c. PRIDMORE ET AL 2,860,331

Nov. 11, 1958 OSCILLOSCOPE DISPLAY METHOD AND CIRCUIT FOR F. M. RADAR SYSTEMS 5 Sheets-Sheet 3 Filed Dec. l5, 1955 ATTORNEYS United States Patent O OSCILLOSCOPE DISPLAY METHOD AND CIRCUIT FOR F. M. RADAR SYSTEMS Thomas C. Pridrnore, Bath, N. Y., and Gordon S. Ley, Plainfield, N. J., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application December 15, 1955, Serial No. 553,397

9 Claims. (Cl. 343-9) The present invention pertains to a circuit that can be utilized to replace the o search and display circuits of existingFM radar systems and which will display all four quantities when the radar system, in which the circuit is connected, is in a search condition. Two mutually bisecting lines, prefera-bly a horizontal line and a vertical line, are produced on the screen of an oscilloscope for each target that the radar system detects. vThe lengthof one of these lines is a determinable function of target range and the length of the other line isa determinable function of target radial velocity. The polarity of the system can be made such that the lines increase or decrease in length with decreasing range and approaching velocity. The intersection of the azimuth and elevation of the target.

` Accordingly, an object of the present invention is the provision of an oscilloscope `display circuit and method that willproduce a display of the ranges, radial velocities,

azimuths, and elevations of targets within radar range.

Another object is to provide an oscilloscope display circuit that `replaces the search circuitry of an `FM radar system. and displays the ranges, radial velocities, azimuths, and elevations of targets within radar range.

A further object of the present inventionis theY provision `of an oscilloscope display circuit that when utilized with an FM radar system will produce a display having one line the amplitude of which is a determinable function of target range and another line the amplitude of which is a determinable functionof target velocity.

Still another object of the presentinvention is `to provide an oscilloscope display `circuit that in` conjunction with an FM radar system will produce a `display of two mutually bisecting lines foreach target that is detected,

, the length of one of these lines `being a determinable function of target range and the length of the other being a determinable function of target radial velocity, `and the point of intersection of thetwo lines being `a deter-minable function `of target azimuth and elevation.`

lOther Yobjects and many of the .attendant advantages of this invention will `be readily appreciatedas thetsame becomes `better understood by reference to the following detailed descriptionwhen vconsidered in conn'ection'with the `accompanying `drawings wherein:

)figs 1(a) :and f1(b) show .a block diagram of atypical til] rice

FM radar system with which the present invention can be utilized, and

Fig. 2 illustrates a block diagram of a preferred embodiment of this invention connected with portions of the FM radar system of Figs. l(a) and l(b).

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Figs. 1(a) and 1(1)) a block diagram of a complete FM radar system. In this block diagram, switches S1, S2, and S3 are shown in the position which they would be during automatic tracking. A CW magnetron 11 operating at about 10,000

mc. is frequency modulated il mc. at a rate between l0 kc. and 20 kc. by modulator 12. This signal passes to an antenna 13 by way of a directional coupler 14 and waveguide 15. The frequency modulation of the magnetron vis sinusoidal, the amount of the deviation is held constant, and the modulating rate is a function of the target range.

Some of the transmitted energy propagates to the target being tracked, is reflected and is picked up by the receiving antenna 17, which is lobed at a 1 ,000 cycle rate by lobing head 18. This energy ows through a standard waveguide 21 into a balanced mixer 22 where it is converted to an I. F. frequency (54.5 mc.{-Fd). Frequency Fd is the doppler frequency due to the relative motion between theradarand target. A low :noise high gain receiver amplifier 23 amplifies the signal from the mixer 22. The gain of thisV amplifier is determined by 'an A. G. C. voltage.

An output from discriminator- 49 is used to generate an A. F. C. voltage in unit 50 to maintain the local oscillator klystron 51 at a frequency of approximately 9,945.5 mc. `(54.5 mc. below the center frequency of the transmitter magnetron). The local oscillatoroutput is split in magic-T 52 and is fed to the receiver balanced mixer 22 and transmitter balanced mixer 24. The cavities 53, 54 and 55 are tuned to the local oscillator frequency and help prevent any of the transmitter energy from leaking to the receiver mixer by way of `theplumbing between the crystal mixers 22 and 24.

A small portion ofthe transmitted signal is obtained by directional coupler 14 and is fed to a balanced mixer 24 to yield a 54.5 mc. LF. signal. This signal is mixed with a 12.5 mc. fixed amplitude, fixed frequency signal (derived from the crystal oscillator 26) in mixer 27 to yield a 42 mc. signal. This signal is delayed by 85 microseconds in the delay line unit 28, after which it is amplified and limited in unit 29 and combined with the received signal in transmitter-receiver mixer 31. The output from this mixer is at a frequency of 12.5 mc.-l-Fd.

Someenergy from the 12.5 mc. crystal oscillator 26 is mixed with a (0.5 mc.- Fc)` signal in unit 32 to obtain a (12.0 mc.+Fc) signal. The symbol Fc denotes a correction frequency which is approximately equal to the .doppler frequency at all times during tracking. The Y outputs of the mixers 31 and 32 are combined .at doppler mixer 33 to yield a (0.5 rnc.+Fd-Fc) output. This signal feeds the velocitychannel,-the range channel, and the position channel in parallel.

In the velocity channel, the signal first passes through an amplifier and discriminator 34 `having a bandwidth about 1 kc. The outputof this unit feeds the lock-up sweep generator 3S which is utilized to lock the system on a target when the radarfsystem is not in a search condition. The output `of generator 3S feeds the reactance tube oscillator 36 which operates on a frequency of `0.5 mc.-Fc. Action of Ethe velocity servo loop is -`.such as Lto keep Fc approximately equal to Fd. The

output frequency from unit 36 is converted inthe velocity measuring circuit 37 to a D. C. voltage of -30 to +30 Yreceiving antenna 17 at all times.

volts which is proportional to relative velocities from -400 to +400 yards per second.

The signal from unit 33 ,also goes to the range channel where it amplified and passed through a discriminator 38 having a balidwidtl-i of approximately; 10O 'l-:c.V In

this unit an A. G. C.'voltage is obtained whichis fedback to unit 23. The output from discriminator 38 feeds a phase comparator 41 which is also fed by 85 micro- `Asecond delay and 90 degree phase shift circuit 42A with a reference signal having a frequency in the'range from -10 kc.4 to 20 kc.

pending upon the range of the target to be tracked. The

signal from reactance tube oscillator 44 Vis mixed with a fixed 200 kc. signal from an oscillator 4S in mixer 46 whose output is the difference frequency which is inthe range from l kc. to 20 kc. This difference frequency n is fed to a range measuring circuit 47 which Vconverts the frequency to `a Voltage from 0-50 volts that is proportional to range of thev targetY in the interval from 04,000 yards. The output frequency from unit 46 is alsofed to the delay line and 'phase shift circuit 42, and is also employe-d to control the rate of deviation of the transmittermodulator 12. Y

vSome of the energy from the doppler mixer 33 goes to Y the position channel where it is first amplified inunit 56, which has a bandwidth of approximately l0 kc., and

is detected in unit 57. The 1000 cycle signal from detector 57 is fed to the azimuth and elevational phase comparator 58. The lobing generator 65 generates the 4 phase 1,000 cycle signal for the lobing head 18 and phase comparator 58. The output from unit 58 is fed to azi- '.muth Yand elevation receiving antenna servo units 59 jwhich mechanically -drive the receiving antenna 17 in sucha direction as to keep it locked on the target being tracked. A servo system 60 is used to keep the transmitting antenna 13 pointed in the same direction as the A slight mis-alignment of the transmitting antenna 13 or some time delay Vinthe transmitter drive servo is not serious because it tsimply reduces the target elimination by some small amount.` The position lock of the radar is unaffected.

When the 4radar system is in a search condition, `the electronic switches S1, S2, and S3 will all be in positions opposite to that shown on the block diagram. Po-

lsition information from a manually operatedsighting station orV from a programmed search unit 61 will be fed l to unit58. During search, unit 62 generates a sawtooth sweep voltage which is fed by way of switch S2 to the -reactance tube oscillator 44 causing it to sweep over the range of frequency from 210 kc. to 220jk`c. Simi- A larly, during a search for the target in velocity, unit 63 generates a sawtooth voltage which isfed to the reactance tube oscillator 26, by way of switch S3,to

vary the frequency aboverand below the nominal half rnc. value by an amount equal to the maximum doppler shiftl expected.

A preferredk embodiment of the presentV invention is shown in Fig. 2 connected to slightly modified range and velocity channels of the FM radar system of Figs. l(a) and l(b), butitjs to `be realized that this invention can be`utilized, as well, with many other types of FM Y inator 34. The time of occurrence of Van outputpuh state, multivibrator 86 energizes switch amplifier 76 whil j and to connect lock-up sweep generator 43 to reactan# Ytube oscillator 44; switch 83 to joinv the vertical dell t nect the output of mixer 46 from the input to /modulatg' y fact that when the radar system is in ase'archin'gop the doppler effect. The output of mixer 33 is thus a l the target radial velocity. This varyingfrequency hai 34 and hence this discriminator will not produce g put except whenthis varying frequency 'passes through L creasing' envelope. Whether Vtheenvelope decreases 76. Sawtooth voltage generator 77 supplies a sawto'odxfl,j voltage wave train to the range and velocity channelre-.l` actance tubes through sequentially operated switches Fl (S-Z) and 79 (S-3) respectively. Generator 77 supplie` a sawtooth voltage wave train to modulator 81 to trol the amplitude of the signal from -oscillator 821m. is applied to either the horizontal or vertical deflecti0l.. system of oscilloscope 74; the energization of switchzf determining upon which deliection systemthe signal i! applied. A sawtooth voltage wave train yfrom genera p 77 is differentiated by differentiator 84V and conductecl` (er bi-stable multivibrator 86, which produces a signaLthit actuates switch amplifier 76. The V,live outputsfralpli switch amplifierV 76 are individually joined toswitchag". 71, 78, 79, 83,`and 87. Leads 88 and 89 connectfthf* output of the azimuth and elevation comparator 58195;.' the vertical and horizontal deflections systems, respectively, of oscilloscope 74 to synchronize the movev4 of the oscilloscope beamV with the movement of anteina 17. Y Y When it is desired to initiate a search operation, embodiment shown Yin Fig. 2 is energized by some switch@ means (not shown), whereupon generator 77 commenta?.V the generation of sawtooth waves. The differentiated kstv!- tooth output from generator 77 .triggers bi-stable mult!- vibrator A86 into one of its two stable states. In

in turn activatesgswitch 71 to couple detector-amplihll circuit 72 to the Z axis control; switch 79 to disconnt lock-up sweep generator 35 from and to connect animate; put'from generator 77 to reactance tube oscillator 13S' switch 78 to disconnect an output of generator 77 V tion system to modulator 81; and switch 87 to discog- 12. This last switching operation is necessary due', toft tion, the range channel is not locked-up and 4magnetron 11 would otherwise undergo frequency modulation a result 0f the output from mixer 46V. The velocityf-c*u nel bandwidth is much too narrow to'function propf with the large deviations ofthe magnetron 'freque` caused by the range channel, thus the disconnecti mixer 46 is required if magnetron 11 is to operateas CW. source without'frequency modulation.VV When'a, get is encountered by the radar `beam duringsearch, tenna 17 receives an echo signalwhich after amplifie tion and' frequency conversionin units 22, 23, gandQL islmixed in mixer 33 with the sweeping output from cillator 36 which has been altered` in frequency in` 32. If, the target has a radial velocity with 'respe the transmitter, therewill be a change in frequency d ing frequency whosemedian frequency is a function`V range much greater thanthe bandwidth of discriminat@l the frequencies contained in the bandwidth of discrij from discriminator 34 with respect to the initiatingpm of generator 77 is thus a function of target velocityfs'V that velocity determines` the median frequencyfofjtif output from mixer 33, The discriminator output is detected and `amplified in unit 72 and energizesjthe axis control to turn the oscilloscope beam on for the ration of this pulse. At the instant that generatorV` triggers bistable multivibrator 86, it transmitsafsa' tooth wave to modulator 81. This sawtooth waveVV a much longer period than a cycle from oscillator 82 i thus the modulated wave' from modulator 81 Vis a'lit frequency wave having the frequency of the input win from oscillator 82, with a constantly increasing or increases with respect to time depends upon the polarity of the slope of the sawtooth wave from generator '77. Of course this high frequency wave is not visible on the `oscilloscope except at the time. when the Z axis control is energized, which time is a function of the radial target velocity. The vertical heighth of a scope pattern isy proportional to the voltage onthe vertical deflection system; hence, when the beam is turned on the vertical pattern will appear as a line whose amplitude is a function of the target radial velocity. This line is actually a large num ber of closely spaced cycle lines which appear as one line due to the high frequency of'the wave from modu lator 3l and the slowness of movement of the scope beam in the brief interval in which the oscilloscope beam turned on.

When the next sawtooth wave is generated in generator 77, bi-stable multivibrator 86 willtrgger into its other stable state. The outputs from switch amplifier 76 then activate: switch 71 to disconnect detector-amplifier circuit 72 from and to connect detector-'amplifier circuit 73 to the Z axis control; switch` 78 to disconnect lock-up sweep generator 43 from and to connect an output from generator 77 to reactance tube oscillator 44; switch 79 to disconnect an output, of generator 77 fromand to connect the` lockfup` sweep generator 35 Vto reactance tube oscillator 36; switch 83 `to decouple the verticalplate system from and` to couple the horizontal plate system to the output of modulator 81; and switch S7 to. join the output of mixer 46 to modulator 12. The operation for range detection is similar to that of velocity detection except that magnetron 11 is now modulated and the rate of modulationis determined by the output frequency of generator 77 to reactance tube oscillator 44. When the received echo signal, 'after amplification and frequency changing, is of a -frequency topass through `discriminator 38. and of proper phase to produce an output from phase comparator 42, detector-amplifier circuit 73 will operate the Z axis lcontrol to turn on the oscilloscope beam. A1 horizontal; linewill` thenyappear on the oscillopscope screen having an amplitude that is a determinable function of range. Thus, two lines will appear on the scope and if `ahigh persistentl screen is-employed there will 'bei simultaneousV patterns of` a horizontal and vertical line for each target. Since the position of the scope `beam is controlled by the antenna position, as in most radar systems utilizing C-scope presentation, the intersection of the two lines Will be an indication of the azimuth and elevation of the target. Although it is not readily apparent, the point of intersection will approximately bisect both lines. The oscilloscope beam moves quite slowly in comparison to the period of thel output from generator 77, thus the beam will not have, moved a detectable amount during the time between th;- generation of a horizontal line and a vertical line. The quiescent point 'about which the vertical line cycles in positive and negative directions by equal amounts, is for practical purposes the quiescent point about which the horizontal line cycles in positive and negative directions in equal amounts. Hence, this quiescent point is the point of intersection for the vertical and horizontal lines land is midway between the ends `of both lines. If it is de sired to have the oscilloscope pattern increase in size with respect to proximity and approaching velocity, the sawtooth wave from generator 77 that feeds modulator 81 should have a positive slope, and if the opposite conditionv is desired, this wave should have a negative slope. It is to be noted that either the horizontal or vertical line can represent range or velocity.

An oscilloscope display circuit has been disclosed which if utilized in an FM radar system will produce a display that is a representation of the velocity, range, azimuth, and elevation of each target within radar range. rwo mutually bisecting lines, which are preferably perpendicular, are produced, the length of one of assoei which is adeterminable function ofV rangeandgthe-length ofthe other ofwhich is a determinable functionofA target radial velocity; The point of intersectiony providesj an indication'of the azimuth andtelevation yof a target.

Obviously many4 modifications and variations off the present invention are possible in the light of the above teachings. It` istherefore to be understood-that within the scope` ofthe appended claimsV the inventio-n may be Y practiced` otherwise than as-speciiically described.

What is claimed is:

l. An oscilloscope display circuit forV use in a frequency modulation radar system having a velocity channel and a range channel, said oscilloscopeV display circuit comprising: means for producing alternate velocity and range sweeping by a frequency modulation radar system, an oscilloscope having horizontal .and vertical deflection systems and a Z axis control, means for'producing a linearly changing signal alternately on said horizontal and vertical. deflection systems in synchronism with the alternate velocity and range sweeping, and means responsive to the output of said velocity channel when the frequency modulation radar system is sweeping in velocity and to the output of said range channel when the frequency modulation radar system is sweepingin range for energizing said Z axis control to turn on the oscilloscope beam for a short interval.

2. An 4oscilloscope display circuit for use with a frequency modulation radar system having a velocity channel and a range channel, said oscilloscope display circuit c-omprising: sweep generator means for producing a sawtooth wave train, switch means for connecting sawtooth waves from said sweep generator means alternately into said velocity channel and said range channel for producing alternate velocity .and range sweeps, an oscilloscope having horizontal and vertical deection systems and a Z axis control, means fo-r initiating a constantly changing voltage simultaneously with the beginning of each sawtooth wave of said sawtooth wave train, means for switching said constantly changing Voltage alternately to said horizontal and vertical deection systems in synchronism with the initiation of the alternate sweeps of velocity and range, and means. for switching the output of said range and velocity channels alternately to said Z axis control.

3. An oscilloscope display circuit for utilization with a frequency modulation radar system having a velocity channel with a discriminator and a sweep osciilator and having a range channel with a phase comparator and a sweep oscillator, said oscilloscope display circuit comprising: sweep generator means for producing a sawtooth wave train; switch means for alternately disconnecting said sweep oscillators from said velocity and range channels, respectively, and for connecting said sawtooth wave train alternately to said sweep oscillators in synchronism with the initiation of the sawtooth waves so that alternate sawtooth waves produce velocity and range sweeps by said sweep oscillators; an Ioscilloscope having horizontal and vertical deliections systems and a Z axis control; means for producing a cycling wave upon the initiation of each sawtooth wave of said sawtooth wave train, said cycling wave having a linearly changing amplitude with respect to time; means for switching said cycling wave alternately to said horizontal and vertical deection systems in synchronism with the initiation of the alternate sweeps in said velocity and range channels; and means for switching the output of said phase comparator to said Z axis control only during the range sweeps and for switching the output of said discriminator to said Z axis control' only during the velocity sweeps.

4. An oscilloscope display circuit for utilization with a frequency modulation radar system having a velocity channel and a range channel and an antenna, said oscilloscope display circuit comprising: Van oscilloscope, means for producing alternate sweeps of velocity and of range by said frequency modulation radar systemrmeans triggered by the output of said range channel during a sweep of range for producing .a line on said oscilloscope the Vlength of which is a determinable function of the time difference between the initiation of the range sweep and the occurrence of an output from said range channel, and means triggered by the output of said Velocity channel during a sweep of velocity for producing a line on said oscilloscope the length of which is a determinable function of the time dilference between the initiation of the velocity sweep and the occurrence of an output from said velocity channel. Y

5. The oscilloscope display circuit of claim 4, and means responsive to the instantaneous position of said antenna for displacing one of said lines as a determinable Y nfunction'of'elevation ofY saidrantennaVY and for'displacingn the other of said lines as a determinable function of the azimuthrof said antenna.

6. An oscilloscope display circuit for utilization with a frequency modulation radar system having a velocity channel and a range channel and an antenna, said oscilloscope display circuitcomprising: an oscilloscope having a horizontal deection system and arvertical detiection system; means for producing alternate sweeps of velocity and of range b y said frequency modulation radar system; means for producing a cycling wave upon the initiation of each sweep of velocity and range, said cycling wave having a linearly changing amplitude With Vrespect to time; means for switching said cycling wave alternately to said horizontal and vertical deections systems in syn- `chronism with the alternate sweeps of velocity and of range; and means triggered by the output of said velocity channel during a sweep of velocity and triggered by the output of said range channel during a sweep of range for turning on the oscilloscope beam for a short interval.

7. The oscilloscope display circuit of claim 6, and

and range, said cycling wave having a linearly changing 8 Y deflection system and a vertical deflection system and la, 11 Z axis control that is normally biased so that no pattelfh appears on the oscilloscope; sweep generator mean'sffqg l producing a sawtooth wave train; velocity switch m for alternately disconnecting and connecting said velocity sweep oscillator from and into said velocity channel for coupling said sawtooth wave train to said velocity oscillator only when said Velocity controllable oscillator isdisconnected from said velocity channel, saidlz velocity switch meansv producing a switching operatic'i-l upon the initiation of each sawtooth in said sawtooth` il Wave train; range switch means for alternately disconnegtfll ing and connecting said range sweep oscillator from into said range channel and for coupling said sawtooth wavetrain to saidY range sweep oscillator only when'sai range sweep oscillator is disconnected from .said rang channel, said range switch means producing a switching o operation upon the initiation of each sawtooth in sawtooth wave train in a manner such that said sawtootliV g, Wave train is coupled to only one sweep oscillator at one time; switch means for connecting said Z axis contr to said discriminator when there is a sweep in velocityAi and to said phase comparator when there is a sweepg'. range; switch means for disconnecting said range chan@ f from said frequency modulation radar system only whg there is a sweep in velocity; means for producinga cling wave upon the initiation of each sweep of veloilj amplitude with respect to time; and means for switchiq said cycling `wave alternately to said horizontal and vettig cal deflection systems in synchronism with the alterna@ sweeps of velocity and range. 9. The oscilloscope display circuit of claim 78,V means responsive to the instantaneous position of sai@ antenna and connected to said horizontal and vertical flection systems for controlling the quiescent position .gg the oscilloscope beam as a determinable function of the azimuth and elevation of said antenna.

References Cited in the file of this patent UNITED STATES PATENTS Locke Feb.'24, i Page Apr; 24, 

